A gas supply device of a semiconductor manufacturing apparatus, etc., is generally configured to switch and supply a large variety of gases to an object to use the gas, such as a process chamber, so that a necessary process gas, whose flow rate is controlled by a flow rate controller provided for each kind of supply gas, is supplied to the object to use the gas. The flow rate measurement of each flow rate controller described above is performed at appropriate time intervals generally by a build-up method (or rate of pressure rise (ROR) method), and flow rate measurement is performed by comparing a set flow rate of the flow rate controller with an actual control flow rate measured by the build-up method, etc.
FIG. 5 and FIG. 6 show examples of conventional flow rate measurement devices and methods of a flow rate controller for a gas supply device. Specifically, in the measurement device and method shown in FIG. 5, first, a flow rate measurement unit U0 including a build-up tank BT with a known inner volume, an inlet on-off valve V1, an outlet on-off valve V2, a pressure detector Pd, and a gas temperature detector Td, is joined to a gas supply line L in a branched form. Next, for example, to measure a flow rate controller MFC1 of a gas supply device GF, first, on-off valves V02, V0n, and V0 are closed and on-off valves V01, V1, and V2 are opened, so as to flow the gas into the tank BT, and a pressure detected value P1 and a temperature detected value T1 at a time t1, in a state where the on-off valves V1 and V2 are opened, or at a time t1 in a state where the on-off valve V2 is closed after the on-off valves V1 and V2 are opened, are measured. Next, a pressure detected value P2 and a temperature detected value T2 are measured Δt seconds after the on-off valve V1 is closed from the opened state of the on-off valves V1 and V2 or Δt seconds after the time t1 in a state where the on-off valve V2 is closed after the on-off valves V1 and V2 are opened.
Then, from the respective measured values described above, a rate of pressure rise ΔP/Δt is obtained, a flow rate Q is calculated based on Q=(ΔP/Δt)×(V/RT), and a flow control value of the flow rate controller MFC1 is confirmed. The flow rate calculation formula is for arithmetically calculating a build-up flow rate into the tank BT on the assumption that the gas is an ideal gas, and V is a total inner volume of the build-up tank VT and the pipe passage on the upstream side, R is a gas constant, and T is a gas temperature inside the tank BT.
On the other hand, in the measurement method shown in FIG. 6, a flow rate measurement unit U1 without the build-up tank is joined to a gas supply line L in a branched form. Then, for example, to measure the flow rate controller MFC1 of the gas supply device GF, first, on-off valves V0, V00, V02, and V0n are closed and on-off valves V01, V1, and V2 are opened to supply the gas at a set flow rate from the flow rate controller MFC1 to the flow rate measurement unit U1, and then, the on-off valve V2 is closed. After the on-off valve V2 is closed, when the pressure detected value of the pressure detector Pd reaches pressure P1, a first measurement is performed to measure the pressure P1 and the temperature T1. Thereafter, when the pressure detected value of the pressure detector Pd reaches P2 (or when a set time of t seconds elapses), a second measurement is performed to measure the pressure P2 and the temperature T2.
In addition, by arithmetically calculating a sum V of a pipe passage inner volume Ve of the portion of the gas supply lines L and Ls from the on-off valve V00, the on-off valve V01, the on-off valve V02, and the on-off valve V0n on the upstream side of the flow rate measurement unit U1 to the on-off valve V1 and an inner volume Vt of the flow passage between the on-off valve V1 and the on-off valve V2 of the flow rate measurement unit U1 based on the flow rate formula Q=(ΔP/Δt)×(V/RT) by using a rate of pressure rise ΔP/Δt obtained by the same measurement method as in the case of FIG. 5, and the flow rate value Q of the flow rate controller MFC1 at that time, the total inner volume V is obtained in advance.
Then, from the respective measured values described above, a gas absolute flow rate Qo at a temperature of 0° C. at 1 atm from the flow rate controller MFC1 is obtained based on the relationship between the inflow mass dG and an elapsed (inflow) time dt of the gas. That is, the inflow mass dG can be expressed by dG=ro·Qo·dt (provided that dt is an elapsed (inflow) time and ro is a specific weight of the gas). Based on the pressures P and temperatures T measured by the first measurement and the second measurement described above, an ideal gas has a relationship of PV=nRT, and by substituting the mass G for the mole number n, the relationship of PV=GRT is established.
Therefore, on the assumption that the gas pressure P1, gas temperature T1, gas mass G1 are measured by the first measurement, and the gas pressure P2, gas temperature T2, and gas mass G2 are measured by the second measurement, the difference in mass G (inflow mass dG) is expressed by dG=G2−G1=P1/T1·V/R−P2/T2·V/R=(P1/T1−P2/T2)·V/R . . . Formula (I), and from the above-described formula dG=ro·Qo·dt, the absolute flow rate Qo of the gas can be calculated by Qo=(P1/T1−P2/T2)·V/R·1/(ro·t). Based on the calculated value Qo, it is determined whether the flow rate control performance of the flow rate controller MFC1 is proper.
In the method shown in FIG. 6, the objects of the invention are (1) to reduce errors of the calculated reference flow rate by using a coefficient that is a compression factor in Formula (1) described above since application of the ideal gas equation becomes difficult depending on the kind of gas, and (2) to determine the timing to start the second measurement after the first measurement based on a pressure rise value when the control flow rate is in the range of 1000 to 2000 Standard Cubic Centimeters per Minute (SCCM) or based on an elapsed time when the control flow rate is in the range of 2 to 1000 SCCM.
In the method shown in FIG. 6, it is also a matter of course that a rate of pressure rise ΔP/Δt is obtained from the respective measured values described above, a flow rate Q is calculated based on Q=(ΔP/Δt)×(V/RT), and it can be determined whether the flow rate control value of the flow rate controller MFC1 is proper based on the calculated value.
The method using the build-up tank BT shown in FIG. 5 has problems including that (1) the flow rate measurement device increases in size (must be made larger) due to the use of the build-up tank BT and it is not possible to downsize the dimensions of the gas supply device, (2) the measured value of the gas temperature inside the tank BT significantly fluctuates according to the position of attachment of the temperature detector Td, (3) the gas temperature T during rise of the gas pressure inside the tank significantly fluctuates and does not become a constant temperature T, and (4) when a temperature change of the outside air is large, the gas temperature during pressure detection changes and fluctuation of the temperature detected value T increases, etc., so that even if the gas is close to an ideal gas, high flow rate measurement accuracy cannot be obtained.
On the other hand, in the method shown in FIG. 6, the valve V1 is provided on the flow-in side of the flow rate measurement unit U1, and via this valve, the unit U1 is joined to the end portion of the branched connection pipe passage Ls. However, this valve V1 is not used for flow rate measurement at all, rather, the presence of this valve V1 poses various problems, namely, that fluid resistance increases, a drive mechanism of the valve V1, for example, an electromagnetic valve and drive fluid piping, etc., become necessary, the component cost and assembly cost increase, an operation delay is caused by the driving performance of the valve V1, and timing adjustment becomes necessary, etc.
In the method shown in FIG. 6, in order to measure a sum volume V of the flow passage inner volume Ve of the fluid supply line L and the branched connection pipe passage Ls and the flow passage inner volume Vt of the flow rate measurement unit U1, the valve V1 is opened and closed twice, and during this time, the inside of the flow rate measurement unit U1 is vacuumed. These valve openings and closings require too many procedures to perform flow rate measurement.